WO2021221624A1

WO2021221624A1 - Three-dimensional printing

Info

Publication number: WO2021221624A1
Application number: PCT/US2020/030386
Authority: WO
Inventors: Adekunle OLUBUMMO; Krzysztof Nauka; Kyle WYCOFF
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-04-29
Filing date: 2020-04-29
Publication date: 2021-11-04

Abstract

The present disclosure relates to fusing agents for 3D printing. The fusing agents comprise: a hydroxyphenyl benzotriazole, surfactant and water. The present disclosure also relates to 3D printing kits. The kits may comprise powder bed material, and fusing agent. The present disclosure also relates to methods for printing a 3D printed object. The methods may comprise selectively applying fusing agent to powder bed material, and irradiating the selectively applied fusing agent with UV radiation to fuse at least a portion of the powder bed material.

Description

THREE-DIMENSIONAL PRINTING

BACKGROUND

[0001] Three-dimensional (3D) printing is an additive printing process used to make three-dimensional solid objects from a digital model. Some 3D printing techniques may be considered additive processes because they involve the application of successive layers of material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Features of examples of the present disclosure will become apparent, by way of example, with reference to Figure 1 , which is a schematic diagram of an example 3D printer that can be used to print a 3D printed object.

DESCRIPTION [0003] In a method of 3D printing, a fusing agent may be selectively applied to a layer of powder bed material. The fusing agent may include a radiation absorber. When the selectively applied fusing agent is irradiated with radiation, the radiation absorber may absorb the radiation and covert it to heat. The heat generated may heat the powder bed material in contact with fusing agent, causing it to fuse or coalesce to form a layer of the 3D printed object. A further layer of powder bed material may be applied and the process repeated layer-by-layer until the 3D printed object is formed.

[0004] Suitable radiation absorbers include near infrared absorbers, for example, carbon black. Carbon black may absorb radiation emitted by, for example, tungsten-halogen (QTH) fusing lamps installed in the 3D printer to fuse particles of the powder bed material together. Carbon black, however, also absorbs wavelengths in the visible spectrum and thus has a discernible color that can be detected in the 3D printed part. Accordingly, it can be more difficult to produce white, transparent or lightly coloured 3D printed parts with near infrared absorbers such as carbon black. [0005] The present disclosure relates to a fusing agent for 3D printing. The fusing agent comprises: a hydroxyphenyl benzotriazole, a surfactant and water.

[0006] The present disclosure also relates to a 3D printing kit. The kit may comprise powder bed material, and fusing agent. The fusing agent comprises: a hydroxyphenyl benzotriazole, a surfactant and water.

[0007] The present disclosure also relates to a method for printing a 3D printed object. The method comprises selectively applying fusing agent to powder bed material, and irradiating the selectively applied fusing agent with UV radiation to fuse at least a portion of the powder bed material. The fusing agent comprises: a hydroxyphenyl benzotriazole, a surfactant and water.

[0008] Hydroxyphenyl benzotriazoles absorb in the UV region. It has been found that hydroxyphenyl benzotriazoles can be used in fusing agents for coalescing or fusing powder bed material during 3D printing. In some examples, hydroxyphenyl benzotriazoles absorb sufficiently strongly in the UV region that fusing or coalescing of the powder bed material can be achieved at relatively low irradiation intensities and/or without having to resort to excessively long irradiation times. In some examples, hydroxyphenyl benzotriazoles may also be used to produce 3D printed parts that are transparent, white or light in colour, as hydroxyphenyl benzotriazoles may have low absorbance, or may be transparent or reflective in the visible spectrum.

[0009] In some examples, the fusing agent may comprise about 1 to about 15 weight % of hydroxyphenyl benzotriazole.

[0010] In some examples, the fusing agent may comprise about 10 to about 50 weight % surfactant. [0011] The surfactant may comprise octyl acetate.

[0012] In some examples, the weight ratio of the hydroxyphenyl benzotriazole to surfactant may be about 1:1 to about 1:10.

[0013] In some examples, the fusing agent may include an organic solvent. The organic solvent may be present in an amount of about 20 to about 70 weight % of the total weight of the fusing agent.

[0014] In some examples, the organic solvent may be selected from at least one of alcohol (including polyhydric alcohols, such as, for example, glycols) and a glycol ether. [0015] In some examples, the fusing agent may comprise about 10 to 50 weight

% water.

[0016] In some examples, the hydroxyphenyl benzotriazole may be 2-(2- hydroxyphenyl)-2h-benzotriazole.

[0017] The UV radiation may have a wavelength of about 300 to 400 nm. In some examples, the UV radiation may be provided by a UV LED source having a wavelength of 365 nm or 395 nm. [0018] The powder bed material may comprise polyamide.

Fusing Agents

[0019] As mentioned above, the fusing agent includes a hydroxyphenyl benzotriazole radiation absorber.

[0020] In some examples, the hydroxyphenyl benzotriazole may have the general formula I below:

[0021] wherein:

[0022] R₁ to R₅ may be independently selected from H, OH or hydrocarbyl, with the proviso that at least one of R₁ to R₅ is OH, and

[0023] R₆ to R₉ may be independently selected from H, hydrocarbyl or halo.

[0024] In some examples, R₆ to R₉ may be independently selected from H or halo. In some examples, one of R₆ to R₉ may be halo and the remainder may be H. In some examples, R₇ may be halo and the remainder of R₆ to R₉ may be H. Suitable halo groups include F, Cl, Br and I, for instance, Cl.

[0025] In some examples, R₄ may be OH. R₁, R₂, R₃ and R₄ may be independently selected from H or hydrocarbyl. In some examples, at least R₃ and R₁ may be H. [0026] In some examples, R₄ may be OH; R₁ and R₃ are each H and either R₄ is

H and R₂ is selected from H or hydrocarbyl, or both R₄ and R₂ are hydrocarbyl. Where R₄ and R₂ are hydrocarbyl, they may be the same or different hydrocarbyls.

[0027] Suitable hydrocarbyl groups include alkyl, aryl and/or -L₁-Ar. L₁ may be a linker, for example, of the formula -[CR_aR_b)_n-, where n is an integer of from 0 to 3 and R_a and R_b are in each instance each independently selected from H or C₁ to C₂ alkyl. Ar may be an aryl group. [0028] Suitable alkyl groups include C₁ to C₁₅ alkyls, for example, C₁ to C₁₀ alkyls or C₁ to C₈ alkyls. In some examples, the alkyl group may be selected from methyl, butyl (e.g. s-butyl or t-butyl), pentyl (e.g. t-pentyl), and tetramethyl butyl (e.g. 1, 1,3,3- tetramethylbutyl).

[0029] Suitable aryl groups include phenyl.

[0030] Suitable -L₁ -Ar groups include groups having the formula -[(CR_aR_b)_n]Ar, where each R_a and R-_b is each independently H or C₁ to C₃ alkyl and n is 1 , 2 or 3, and Ar may be an aryl group, for example, phenyl. In some examples, the L₁-Ar group may be -C(CH₃)₂C₆H₅. [0031] In some examples, the hydroxyphenyl benzotriazole may have the formula

II below:

[0032] R₂ and R₄ are as described above and R^* may be H or halo. In some examples, R* is R₇. In some examples, R* is R₇ and is H or halo (e.g. Cl). For example, the hydroxyphenyl benzotriazole may have the formula III below:

[0033] R₇ may be H or Cl. [0034] R₂ and R₄ may be independently selected from H or hydrocarbyl, where suitable hydrocarbyls include alkyl, aryl or - L₁-Ar as described above.

[0035] Suitable alkyl groups include C₁ to C₁₅ alkyls, for example, C₁ to C₁₀ alkyls or C₁ to C₈ alkyls. In some examples, the alkyl group may be selected from methyl, butyl (e.g. s-butyl or t-butyl), pentyl (e.g. t-pentyl), and tetramethyl butyl (e.g. 1, 1,3,3- tetramethylbutyl).

[0036] Suitable aryl groups include phenyl. [0037] Suitable -L₁-Ar groups include groups having the formula -[(CR_aR_b)_n]Ar, where each R_a and R_b is each independently H or C₁ to C₃ alkyl and n is 1 , 2 or 3, and Ar may be an aryl group, for example, phenyl. In some examples, the - L₁-Ar group may be -C(CH₃)₂C₆H₅. [0038] Suitable hydroxyphenyl benzotriazoles include:

2-(2H-Benzotriazol-2-yl)-4-methylphenol

2-(2H-Benzotriazol-2-yl)-4,6-bis(2-phenyl-2-propanyl)phenoi

2-(2H-Benzotriazol-2-yl)-4,6-di-tert-butylphenol 2-(5-Chloro-2H-benzotriazol-2-yl)-4-methyl-6-di-tert-butylphenol

2-(5-Chloro-2H-benzotriazol-2-yl)-4,6-di-tert-butylphenol 2-(2H-Benzotriazol-2-yl)-4,6-di-tert-pentylphenol

2-(2H-Benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol

2-(2H-Benzotriazol-2-yl)-6-(sec-butyl)-4-(tert-butyl)phenol

2-(2H-Benzotriazol-2-yl)-6-(2-phenyl-2-propanyl)-4-(2,4,4-trimethyl-2- pentanyl)phenol

[0039] In some examples, the fusing agent may include bis-benzotriazolyl tetramethylbutylphenol. In some examples, the fusing agent may not include bis- benzotriazolyl tetramethyl butyl phenol. In some examples, the fusing agent may not include bis-benzotriazolyl tetramethylbutylphenol as the sole radiation absorber.

[0040] In some examples, the concentration of hydroxyphenyl benzotriazole in the fusing agent can be from about 0.1 wt% to about 20 wt% of the fusing agent. In one example, the concentration of absorber in the fusing ink can be from about 0.5 wt% to about 18 wt%. In another example, the concentration can be from about 1 wt% to about 15 wt%. In yet another example, the concentration can be from about 1 .5 wt% to about 10 wt%, for example, 2 to 8 wt % or 3 to 7 wt % of the total weight of the fusing agent. In some examples, the concentration can be 4 to 6 wt % of the total weight of the fusing agent.

[0041] The hydroxyphenyl benzotriazole may absorb UV. For example, the hydroxyphenyl benzotriazole may absorb wavelengths in the range of about 200 to about 400 nm, for example, from about 350 to about 400 nm, for example, about 360 to about 395 nm.

[0042] The hydroxyphenyl benzotriazole may be transparent at least to wavelengths of above about 400 nm, for instance, above about 420 nm, for example, about 450 nm to about 3000 nm. In some examples, the hydroxyphenyl benzotriazole may be transparent to light in the visible range (e.g. about 400 to about 750 nm). In some examples, the hydroxyphenyl benzotriazole may reflect light in the visible range. In some examples, the hydroxyphenyl benzotriazole may be substantially transparent In some examples, the hydroxyphenyl benzotriazole may be substantially white.

[0043] The hydroxyphenyl benzotriazole may have a low toxicity. The fusing agent may be used to produce 3D printed objects used in, for example, food applications or in products that are intended for skin contact.

[0044] The resulting 3D printed object may contain hydroxyphenyl benzotriazole. The concentration of hydroxyphenyl benzotriazole in the 3D printed object may be less than about 0.1 weight %. The hydroxyphenyl benzotriazole may provide some UV resistance to the 3D printed object, reducing the risk of its decomposition under UV light. This may make the fusing agent of the present disclosure suitable for producing 3D printed objects intended for outdoor use.

[0045] The fusing agent may include water. Water may be present in an amount of about 0.5 to about 60 weight %, for example, about 1 to about 55 weight %, about 3 to about 50 weight %, about 5 to about 45 weight %, about 10 to about 40 weight %, about 12 to about 35 weight %, about 15 to about 30 weight % or about 15 to about 25 weight %.

[0046] In some examples, a co-solvent may also be present. The co-solvent may comprise an organic solvent. An organic solvent may be present in an amount of about 10 weight % to about 70 weight %, for example, about 15 weight % to about 65 weight %, about 20 weight % to about 60 weight % or about 25 to about 50 weight %, about 30 to about 45 weight % of the total weight of the fusing agent.

[0047] Examples of suitable organic solvents include aliphatic alcohols, aromatic alcohols, glycol ethers, polyglycol ethers, caprolactams, formamides, acetamides, and long chain alcohols. Examples of such compounds include primary aliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C₆-C₁₂) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. Specific examples of solvents that can be used include 2-pyrrolidinone, N-methylpyrrolidone, 2-hydroxyethyl-2-pyrrolidone, 2- methyl-1, 3-propanediol, tetraethylene glycol, 1,6-hexanediol, 1 ,5-hexanediol and 1,5- pentanediol, ethanol, pentanol, ethylene glycol, propylene glycol, and diethylene glycol butyl ether.

[0048] In some examples, the fusing agent comprises an organic solvent selected from alcohols and glycol ethers. Where alcohols are used, the alcohols may be monohydric or polyhydric alcohols (e.g. glycols). In some examples, the fusing agent comprises at least two organic solvents. In some examples, the fusing agent comprises alcohol and glycol ether. The total amount of alcohol and glycol ether may be about 10 weight % to about 70 weight %, for example, about 15 weight % to about 65 weight %, about 20 weight % to about 60 weight % or about 25 to about 50 weight %, about 30 to about 45 weight % of the total weight of the fusing agent.

[0049] Where an alcohol is used, the alcohol may be used in an amount of 5 to 50 weight %, for example, 5 to 40 weight %, 10 to 30 weight % of the total weight of the fusing agent. [0050] Suitable alcohols include C₁ to C₁₀ alcohols, for example, C₂ to C₈ alcohols, or C₄ to C₆ alcohols. Monohydric and polyhydric alcohols may be employed. Examples of suitable polyhydric alcohols include glycols. Suitable glycols include C₂ to C₁₀ glycols, for example, C₂ to C₈ glycols. Examples of suitable alcohols include ethanol, pentanol, ethylene glycol and propylene glycol. In one example, the alcohol may be pentanol. In some examples, the alcohol may be used to facilitate bubble formation when applying the fusing agent using a printhead.

[0051] Where a glycol ether is used, the glycol ether may be used in an amount 5 to 50 weight %, for example, 5 to 40 weight %, 10 to 30 weight % of the total weight of the fusing agent.

[0052] Suitable glycol ethers include alkylene glycol ethers and dialkylene glycol ethers. Suitable alkylene glycol ethers include ethylene and propylene glycol ethers. The alkylene glycol ethers may be alkylene glycol monoalkyl ethers or alkylene glycol monoaryl ethers.

[0053] Suitable dialkylene glycol ethers include diethylene glycol ethers and dipropylene glycol ethers. The dialkylene glycol ethers may be dialkylene glycol alkyl ethers. The dialkylene glycol alkyl ethers may be dialkylene glycol (C₁ to C₄) alkyl ethers, for example, diethylene glycol (C₁ to C₄) alkyl ethers.

[0054] Examples of suitable glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, propylene glycol methyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether and dipropyleneglycol methyl ether.

[0055] In one example, the glycol ether may be diethyleneglycol butyl ether.

[0056] Where alcohol and glycol ether are used, the alcohol may be used in an amount of 5 to 50 weight %, for example, 5 to 40 weight %, 10 to 30 weight % of the total weight of the fusing agent, and the glycol ether may be used in an amount 5 to 50 weight %, for example, 5 to 40 weight %, 10 to 30 weight % of the total weight of the fusing agent. The ratio of alcohol to glycol ether may be about 1 :2 to about 2:1 , for example, about 2:3 to about 3:2, or about 4:5 to about 5:4.

[0057] In an example, the fusing agent may comprise pentanol in an amount of 5 to 50 weight %, for example, 5 to 40 weight %, 10 to 30 weight % of the total weight of the fusing agent, and diethyleneglycol butyl ether in an amount 5 to 50 weight %, for example, 5 to 40 weight %, 10 to 30 weight % of the total weight of the fusing agent.

[0058] In some examples, the fusing agent may comprise alcohol, glycol ether and 2-pyrrolidinone as organic solvent. Where 2-pyrrolidone is employed, it may be present in an amount of about 0.5 to about 20 weight %, for example, about 1 to about 15 weight %, about 2 to 10 weight %, or about 5 to about S weight % of the total weight of the fusing agent.

[0059] The fusing agent comprises an surfactant. The surfactant may be non- ionic. The surfactant may be an ester. In some examples, the surfactant may be an alkyl alkanoate. The ester may have 4 to 25 carbon atoms, for example, 6 to 20 carbon atoms, 8 to 15 carbon atoms. The alkyl group of the alkanoate may have a carbon chain length of 1 to 25 carbon atoms, for example, 2 to 20 carbons, 3 to 15 carbon atoms or 5 to 12 carbon atoms. The alkanoate group of the alkyl alkanoate may have 2 to 8 carbon atoms. In some examples, the surfactant may be octyl acetate.

[0060] The surfactant may be present in an amount of about 8 to about 60 weight % of the fusing agent, for example, about 10 to about 55 weight %, about 12 to about 50 weight %, about 15 to about 45 weight %, about 15 to about 40 weight %, about

18 to about 35 weight %, about 20 to 3 weight % or about 20 to 30 weight % of the total weight of the fusing agent.

[0061] In some examples, the surfactant may comprise an ester, for example, an alkyl alkanoate (e.g. octyl acetate). The ester, for example, alkyl alkanoate (e.g. octyl acetate) may be present in an amount of about 8 to about 60 weight % of the fusing agent, for example, about 10 to about 55 weight %, about 12 to about 50 weight %, about 15 to about 45 weight %, about 15 to about 40 weight %, about 18 to about 35 weight %, about 20 to 3 weight % or about 20 to 30 weight % of the total weight of the fusing agent.

[0062] The surfactant may facilitate the dispersion or dissolution of the hydroxyphenyl benzotriazole in the liquid carrier of the fusing agent.

[0063] The weight ratio of hydroxyphenyl benzotriazole to surfactant (e.g. octyl acetate) may be about 1:1 to about 1: 20, for example, about 1 :2 to about 1:15, about 1 :3 to about 1 :10, about 1 :4 to about 1 :8, or about 1 :5 to about 1 :7, for example, about 1:6. [0064] A further surfactant can also be present in the fusing agent. Examples of such further surfactants include alkyl polyethylene oxides, alkyl phenyl polyethylene oxides, polyethylene oxide block copolymers, acetylenic polyethylene oxides, polyethylene oxide (di)esters, polyethylene oxide amines, protonated polyethylene oxide amines, protonated polyethylene oxide amides, dimethicone copolyols, substituted amine oxides, fluorosurfactants, sulphonated surfactants and the like. Other surfactants can include liponic esters such as Tergitol™ 15-S-12, Tergitol™ 15-S-7 available from Dow Chemical Company, LEG-1 and LEG-7; Triton™ X-100; Triton™ X-405 available from Dow Chemical Company; and sodium dodecylsulfate.

[0065] The amount of further surfactant may be present in an amount of up to about 5 weight %, for example, about 0.2 to about 5 weight %

[0066] The total amount of surfactant may be about 8 to about 60 weight % of the fusing agent, for example, about 10 to about 55 weight %, about 12 to about 50 weight %, about 15 to about 45 weight %, about 15 to about 40 weight %, about 18 to about 35 weight %, or about 20 to 35 weight % of the total weight of the fusing agent.

[0067] Various other additives can be employed to optimize the properties of the fusing agent for specific applications. Such additives can be present at from about 0.01 wt% to about 20 wt% of the fusing agent. Examples of these additives are those added to inhibit the growth of harmful microorganisms. These additives may be biocides, fungicides, and other microbial agents, which can be used in inkjet formulations. Examples of suitable microbial agents include NUOSEPT® (Nudex, Inc.), UCARCIDE™ (Union carbide Corp.), VANCIDE® (R.T. Vanderbilt Co.), PROXEL® (ICI America), and combinations thereof. [0068] Sequestering agents, such as EDTA (ethylene diamine tetra acetic acid), may be included to eliminate the deleterious effects of heavy metal impurities. Buffers may also be used to control the pH of the composition. Viscosity modifiers may also be present. [0069] The fusing agent can have a temperature boosting capacity. This temperature boosting capacity may be used to increase the temperature of the powder bed material containing the fusing agent to above its melting or softening point. As used herein, “temperature boosting capacity” refers to the ability of a fusing agent to convert UV energy into thermal energy. When fusing agent is applied to the powder bed material (e.g. by printing), this temperature boosting capacity can be used to increase the temperature of the treated (e.g. printed) portions of the powder bed material over and above the temperature of the untreated (e.g. unprinted) portions of the powder bed material. The particles of the powder bed material can be at least partially bound or coalesced when the temperature increases to or above the melting point of the polymer. It has been found that fusing agents of the present disclosure can be used to coalesce polymer with a high resolution, such that untreated portions of the powder bed material remain unfused.

[0070] As used herein, “melting point” refers to the temperature at which a polymer transitions from a crystalline phase to a pliable, amorphous phase. Some polymers do not have a single melting point, but rather have a range of temperatures over which the polymers soften. When the fusing agent is selectively applied to at least a portion of the polymer powder, the fusing agent can heat the treated portion to a temperature at or above the melting or softening point, while the untreated portions of the polymer powder remain below the melting or softening point. This allows the formation of a solid 3D printed part, while the loose powder can be easily separated from the finished printed part.

[0071] In one example, the fusing agent can have a temperature boosting capacity from about 10°C to about 70°C for a polymer with a melting or softening point of from about 100°C to about 350°C. If the powder bed is at a temperature within about 10°C to about 70*0 of the melting or softening point, then such a fusing agent can boost the temperature of the printed powder up to the melting or softening point, while the unprinted powder remains at a lower temperature. In some examples, the powder bed can be preheated to a temperature from about 10°C to about 70°C lower than the melting or softening point of the polymer. The fusing agent can then be applied (e.g. printed) onto the powder and the powder bed can be irradiated with e.g. UV to coalesce the treated (e.g. printed) portion of the powder.

[0072] The fusing agent can be applied, for example, by printing with a fluid or inkjet printhead, for example, a thermal or piezoelectric printhead. Accordingly, the fusing fluid can be applied with precision to selected areas of the powder bed material to form a layer of the 3D printed object. After applying the fusing agent, the powder bed material can be irradiated with radiant energy. The hydroxyphenyl benzotriazole can absorb this energy and convert it to heat, thereby heating any powder bed material particles in contact with the radiation absorber of the fusing agent. An appropriate amount of radiant energy can be applied so that the area of the powder bed material that is printed with the fusing agent can heat up enough to bind or fuse the e.g. polymer particles. This can consolidate the particles into a solid layer. The powder bed material that is not printed with the fusing agent can remain as a relatively loose powder.

[0073] The process of forming a single layer by applying fusing agent and bed of powder bed material can be repeated with additional layers of fresh powder bed material to form additional layers of the 3D printed object. This can allow the final 3D printed object to be built one layer at a time.

[0074] In the printing process, the powder bed material surrounding the 3D printed object can act as a support material for the object. When the 3D printing is complete, the object can be removed from the bed and any loose powder bed material on the object can be removed.

[0075] In the printing process, UV radiation having wavelengths of about 250 to about 400 nm may be employed, for example, from about 350 to about 400 nm, for example, about 360 to about 395 nm. In some examples, the UV radiation may be supplied from a UV LED source. The UV LED source may have wavelengths of, for example, 365 nm or 395 nm. [0076] As mentioned above, hydroxy phenyl benzotriazoles can be effective absorbers of UV radiation. Thus, in some examples, fusing or coalescing of the powder bed material can be achieved without exposing the powder bed material to excessively high UV intensities and/or prolonged periods of UV irradiation. In some examples, the intensity and/or duration of UV radiation may be controlled relative to the amount of fusing agent that is applied to a layer(s) of build material.

[0077] In some examples, the hydroxyphenyl benzotriazole may be relatively more effective at absorbing UV radiation having relatively short wavelengths, for example, of less than about 395 nm, less than about 380 nm (e.g. about 365 nm). The intensity of UV radiation and/or the duration of irradiation may be varied depending on the wavelength of UV radiation employed and/or the amount of fusing agent applied to the layer(s) of build material. [0078] By way of example, suitable intensities of UV radiation can range from about 5 to about 20 W/cm², for example, about 8 to about 15 W/cm². The duration of irradiation may be less than about 5 seconds, for example, less than about 3 seconds, less than about 2 seconds, less than about 1.5 seconds, or less than about 1 second.

Powder Bed Material

[0079] The powder bed material (also referred to as “build material”) is in the form of particles. The powder bed material may be polymeric powder bed material.

[0080] The particles may have an average particle size of at least about 10 μm for example, at least about 15 μm, at least about 20 μm, at least about 30 μm, at least about 40 μm or at least about 50 μm. The particles may have an average particle size of at most about 120 about, for example, at most about 110 μm, at most about 100 μm, at most about 90 μm, at most about 80 μm or at most about 75 μm.

[0081] In some examples, the powder bed material may have an average particle size of from about 10 to about 120 μm, for example, about 15 to about 110 μm. In some examples, the powder bed material may have an average particle size of from about 20 to about 100 μm, about 30 to about 90 μm, about 40 to about 80 μm or about 50 to about 75 μm. As used in the present disclosure, “average” with respect to properties of particles refers to a volume average unless otherwise specified. Accordingly, "average particle size” refers to a volume average particle size. Additionally, “particle size” refers to the diameter of spherical particles, or to the longest dimension of non-spherical particles. Particle size may be determined by any suitable method, for example, by laser diffraction spectroscopy.

[0082] In accordance with some examples, the volume-based particle size distribution of the powder bed material can be as follows: D50 can be from about 45 μm to about 75 μm, from about 55 μm to about 65 μm, or about 60 μm; D10 can be from about 20 μm to about 50 μm, from about 30 μm to about 40 μm, or about 35 μm; and D90 can be from about 75 μm to about 100 μm, from about 80 μm to about 95 μm, or about 90 μm. "D50" is defined as the median particle diameter (by volume). "D10" is defined as the tenth-percentile by volume of powder that is below a given particle size, e.g., from about 20 μm to about 50 μm. "D90" is defined as the ninetieth-percentile by volume of powder that is below a given particle size, e.g., about 75 μm to about 100 μm.

[0083] In one example, the particle size distribution of the powder bed material is as follows: a. D50 is from about 45 μm to about 70 μm, b. D10 is from about 20 μm to about 50 μm, and c. D90 is from about 75 μm to about 100 μm.

[0084] In certain examples, the particles of the powder bed material can have a variety of shapes, such as substantially spherical particles or irregularly-shaped particles. In some examples, the particles can be capable of being formed into 3D printed parts with a resolution of about 10 to about 120 μm, for example about 20 to about 100 μm or about 20 to about 80 μm. As used herein, “resolution” refers to the size of the smallest feature that can be formed on a 3D printed part. The particles can form layers from about 10 to about 120 μm or 100 μm thick, allowing the fused layers of the printed part to have roughly the same thickness. This can provide a resolution in the z-axis direction of about 10 to about 100 μm. The particles can also have a sufficiently small particle size and sufficiently regular particle shape to provide about 10 to about 100 μm resolution along the x-axis and y-axis.

[0085] In some examples, the powder bed material comprises a polymer powder, for instance, a thermoplastic polymer powder. The polymer can have a melting or softening point from about 70°C to about 350°C. In further examples, the polymer can have a melting or softening point from about 150°C to about 200°C. A variety of thermoplastic polymers with melting points or softening points in these ranges can be used. For example, the polymer powder can be a polyamide. Suitable polyamides include PA- 6, PA- 9, PA-11 , PA-12, PA-66 and PA-612. Other suitable polymer powders include polyethylene powder, wax, thermoplastic polyurethane powder, acrylonitrile, butadiene styrene powder, amorphous polyamide powder, polymethylmethacrylate powder, ethylene-vinyl acetate powder, polyacrylate powder, silicone rubber, polypropylene powder, polyester powder, polycarbonate powder, copolymers of polycarbonate with acrylonitrile butadiene styrene, copolymers of polycarbonate with polyethylene terephthalate polyether ketone powder, polyacrylate powder, polystyrene powder, or mixtures thereof. In an example, the polymer powder can be a polyamide powder, e.g. PA-11 or PA-12. In another example, the polymer powder can be thermoplastic polyurethane.

[0086] The powder bed material may also include an anti-oxidant. The antioxidant can be sterically hindered phenol derivatives. The anti-oxidant can, for example be in the form of fine particles, e.g., 5 μm or less, that are e.g. dry blended with the remaining particles of the powder bed material. The anti-oxidant may be present at a concentration of at least about 0.01 wt %, for example, at least about 0.05 wt %, at least about 0.1 wt % or at least about 0.2 wt %. The anti-oxidant may be present at a concentration of at most about 2 wt %, for example, at most about 1.5 wt % or at most about 1 wt %. In some examples, the anti-oxidant may be present in an amount of e.g., from about 0.01 wt% to about 2 wt% or from about 0.2 wt% to about 1 wt% of the powder bed material. The powder bed material can, in some cases, also comprise a filler. The filler can include inorganic particles such as alumina, silica, glass, and/or other similar fillers.

In some examples, the filler can include a free-flow filler, anti-caking filler, or the like. Such fillers can prevent packing of the powder bed material, and/or coat the particles of the powder bed material and smooth edges to reduce inter-particle friction, and/or absorb moisture. In some examples, a weight ratio of thermoplastic polymer to filler particles in the powder bed material can be from about 99: 1 to about 1 :2, from about 10: 1 to about 1 :1, or from about 5:1 to about :1. Detailing Agents

[0087] In some examples, a detailing agent may be used. The detailing agent can be capable of reducing the temperature of the powder bed material onto which the detailing agent is applied. In some examples, the detailing agent can be printed around the edges of the portion of the powder bed material that is printed with the fusing agent. The detailing agent can increase selectivity between the fused and unfused or partially unfused portions of the powder bed by reducing the temperature of the powder around the edges of the portion to be fused. [0088] In some examples, the detailing compound can be a solvent that evaporates at the temperature of the powder bed. In some cases the powder bed can be preheated to a preheat temperature within about 10 °C to about 70 °C of the fusing temperature of the polymer powder. Depending on the type of polymer powder used, the preheat temperature can be in the range of about 90 °C to about 200 °C or more. The detailing compound can be a solvent that evaporates when it comes into contact with the powder bed at the preheat temperature, thereby cooling the printed portion of the powder bed through evaporative cooling. In certain examples, the detailing agent can include water, co-solvents, or combinations thereof.

[0089] Non-limiting examples of co-solvents for use in the detailing agent can include xylene, methyl isobutyl ketone, 3-methoxy-3-methyl-1 -butyl acetate, ethyl acetate, butyl acetate, propylene glycol monomethyl ether, ethylene glycol mono tert- butyl ether, dipropylene glycol methyl ether, diethylene glycol butyl ether, ethylene glycol monobutyl ether, 3-Methoxy-3-Methyl-1 -butanol, isobutyl alcohol, 1 ,4- butanediol, N,N-dimethyl acetamide, and combinations thereof. [0090] In some examples, the detailing agent can be mostly water. In a particular example, the detailing agent can be about 85 wt% water or more. In further examples, the detailing agent can be about 95 wt% water or more. In still further examples, the detailing agent can be substantially devoid of radiation absorbers. That is, in some examples, the detailing agent can be substantially devoid of ingredients that absorb enough radiation energy to cause the powder to fuse. In certain examples, the detailing agent can include colorants such as dyes or pigments, but in small enough amounts that the colorants do not cause the powder printed with the detailing agent to fuse when exposed to the radiation energy. [0091] The detailing agent can also include ingredients to allow the detailing agent to be jetted by a fluid jet printhead. In some examples, the detailing agent can include additives such as those in the fusing agent described above. These ingredients can include a liquid vehicle, surfactant, dispersant, co-solvent, biocides, viscosity modifiers, materials for pH adjustment, sequestering agents, preservatives, and so on. These ingredients can be included in any of the amounts described above.

3D Printing [0092] FIG. 1 is a schematic diagram of an example 3D printer 100. The 3D printer 100 may also be termed a 3D fabricating device, a 3D additive manufacturing device, etc., and may be implemented to fabricate 3D parts.

[0093] The 3D printer 100 may include a delivery device 110 that may be controlled to deposit a fusing agent 112 onto selected areas of a layer 122 of particulate powder bed material 120. As discussed above, the fusing agent 112 comprises hydroxyphenyl benzotriazole. This is a radiation absorber that absorbs UV light, converting it to heat. Accordingly, when fusing agent 112 is applied to the powder bed material 120 and irradiated with UV, the heat produced can soften or melt the particles of powder bed material 120 in contact with the fusing agent 12, causing the particles to coalesce. [0094] The UV radiation employed may include wavelengths that range from about 200 nm to about 400 nm. In other examples, the wavelengths may range from about 320 nm to about 380 nm. In still other examples, wavelengths may include wavelengths that fall below 420 nm. [0095] According to an example, the hydroxyphenyl benzotriazole in the fusing agent 112 may be colorless in a visible spectrum, i.e., transparent between the UV and IR wavelength ranges, and the powder bed material particles 120 may have a white or other light color. In another example, the hydroxyphenyl benzotriazole in the fusing agent 112 may be white (i.e., may reflect all light in a visible spectrum). In one regard, therefore, the powder bed material particles 120 may be fused together to form a white or other light-colored part without the hydroxyphenyl benzotriazole in the fusing agent 112 adding excessive color to the formed part.

[0096] According to an example, the delivery device 110 may be scanned across the layer 122 in one or multiple directions to enable droplets of the fusing agent 112 to be delivered to selected areas of the layer 122 of powder bed material particles 120. In addition or in other examples, the delivery device 110 may remain stationary and the layer 122 may move with respect to the fluid delivery device 110. In still other examples, both the delivery device 110 and the layer 122 may move with respect to each other. According to examples, the delivery device 110 may be a thermal inkjet printhead, a piezoelectric printhead, or the like, although the delivery device 110 may include other types of fluid delivery devices.

[0097] The layer 122 of powder bed material particles 120 may be formed through operation of a re-coater (not shown) to spread a plurality of powder bed material particles 120 to form the layer 122 of powder bed material particles 120 over a surface 124. The surface 124 may be a build platform ora previously formed layer 122 of powder bed material particles 120. [0098] The re-coater may have a cylindrical configuration and may be rotated and translated over the powder bed material particles 120 to form the powder bed material particles 120 into the layer 122. By way of example, the re-coater may be formed of a metallic material and may have a polished or a textured surface. The re- coater may be employed to form the layer 122 to have a substantially uniform thickness across the surface 124. In other examples, the re-coater may be a doctor blade or other suitable device for spreading the powder bed material particles 120 into the layer 122. In an example, the thickness of the layer 122 may range from about 90 μm to about 110 μm, although thinner or thicker layers may also be used. For example, the thickness of the layer 122 may range from about 20 μm to about 200 μm or from about 50 μm to about 200 μm.

[0099] As also shown in FIG. 1 , the 3D printer 100 may include a light source 130 to apply light 132 onto the deposited fusing agent 112 and the layer 122 of powder bed material particles 120. The light source 130 may be a light emitting diode, a laser, a lamp, or the like. By way of particular example, the light source 130 may be strobe lamp, such as a Xenon (Xe) strobe lamp. In addition, the light source 130 may emit light 132 across a wide spectrum of wavelengths. For instance, the light source 130 may emit light 132 that ranges in wavelengths from around the UV wavelength range to nearly the infrared (IR) range. In this example, a filter may be employed to block light having wavelengths that are above the UV wavelength range, e.g., light having wavelengths above about 400 or 420 nm. In other examples, the light source 130 may emit light across a narrower range of wavelengths, e g., around the UV wavelength range. Although a single light source 130 has been depicted in FIG. 1 , the 3D printer 100 may include multiple light sources 130 that emit light at the same wavelengths with respect to each other or at different wavelengths with respect to each other. For instance, one of the multiple light sources 130 may emit light around the UV wavelength range and another one of the multiple light sources 130 may emit light around the IR wavelength range.

[0100] Although not shown, a processor may control the light source 130 to apply short bursts of light 132. For instance, the processor may control the light source 130 to flash a single time at the certain energy level, e.g., between about 7 J/cm² and about 20 J/cm² for about 15-20 ms. In other examples, the processor may vary the number of times and/or the durations at which the light source 130 is flashed. For instance, the number of times and/or durations may vary for different types of materials, particle sizes, and/or distribution of powder bed material particles 120. According to examples, the light source 130 may be a single energy source that may be operated at multiple energy levels. In other examples, the light source 130 may be a plurality of light sources. In any of these examples, the light source 130 may be a photonic fusing source, such as, a Xenon (Xe) strobe lamp, although other types of strobe lamps may be implemented.

[0101] In some examples, the light source 130 may emit light 132 simultaneously onto a large section of the deposited fusing agent 112. In these examples, the light source 130 may be positioned at a fixed location above the layer 122 of the powder bed materia] particles 120. In other examples, the light source 130 may be scanned across the layer 122 in one or multiple directions to enable droplets of the fusing agent 112 to be delivered to selected areas of the layer 122 of powder bed material particles 120. In addition or in other examples, the delivery device 110 may remain stationary and the layer 122 of powder bed material particles 120 may move with respect to the delivery device 110. In still other examples, both the delivery device 110 and the layer 122 may move with respect to each other.

[0102] The hydroxyphenyl benzotriazole in the fusing agent 112 may absorb light around the UV wavelength range from the applied light 132. Absorption of the light 132 may cause the hydroxyphenyl benzotriazole in the fusing agent 112 to absorb light around the UV wavelength range from the applied light 132 and may become heated to a temperature that causes the powder bed material particles 120 upon which fusing agent 112 has been deposited to melt. Additionally, the melted powder bed material particles 120 may fuse together following cessation of the application of the light 132 and subsequent cooling of the powder bed material particles 120. As the fusing agent 112 may merely convert the absorbed light into heat and may convey the heat to the underlying powder bed material particles 120, the powder bed material particles 120 may melt and fuse together without their chemical compositions changing.

[0103] According to an example, the fusing agent 112 and the light source 130 may be tuned with respect to each other with regard to the powder bed material particles 120. That is, the fusing agent 112 and the light source 130 that may operate together to cause the powder bed material particles 120 to adequately melt may be included in the 3D printer 100. For instance, the wavelengths at which the light source 130 outputs light 132 may be tuned to the wavelengths at which the hydroxyphenyl benzotriazole in the fusing agent 112 absorbs light. In addition, or in other examples, the volumes at which the fusing agent 112 are applied to the powder bed material particles 120 may be varied depending upon the energy level applied by the hydroxyphenyl benzotriazole in the fusing agent 112 and/or characteristics, such as material, size, distribution, etc., of the powder bed material particles 120.

[0104] Moreover, or in other examples, the amount of energy applied onto the layer 122 of the powder bed material particles 120 by the light source 130 may be varied depending upon the light absorption properties of the hydroxyphenyl benzotriazole in the fusing agent 112 and/or characteristics, such as material, size, distribution, etc., of the powder bed material particles 120. Accordingly, for instance, either or both of the volume of fusing agent 112 and the energy output by the light source 130 may be varied depending upon the properties of the powder bed material particles 120. That is, either or both of the delivery device 110 and the light source 130 may be controlled to cause the powder bed material particles 120 to sufficiently melt.

EXAMPLES [0105] A fusing agent was prepared having the composition shown in the Table 1 below:

[0106] Samples in the form of rectangular plaques were printed using PA-12 powder as the powder bed material using an HP Multi-Jet Fusion printer. The fusing agent of Table 1 above was selectively applied to the powder bed material and exposed to UV light of 365 nm, causing the treated portions of powder bed material to coalesce to form a layer of the 3D printed sample. The process was repeated until the desired sample thickness was achieved. [0107] The procedure was repeated by applying the fusing agent at range of print densities (Contone levels - 128, 256 and 512, respectively) and by irradiating at intensities ranging from 9.6 W/cm² to 12 W/cm² for 0.5 to 2 seconds per pass.

[0108] In all instances, the fusing agent absorbed sufficient energy to coalesce powder bed material that was treated with the fusing agent with good/excellent selectivity. Untreated powder bed material surrounding the samples exhibited no signs of sintering or fusing. The hydroxyphenyl benzotriazole absorbed strongly in the UV region, allowing printing to be carried out even at relatively low irradiation intensities and/or durations of UV exposure. Definitions

[0109] It is noted that, as used in this specification and the appended claims, the singular forms ''a,'' "an," and "the" include plural referents unless the content clearly dictates otherwise.

[0110] As used herein, the term “about” is used to provide flexibility to a range endpoint by providing that a given value may be “a little above” or “a little below" the endpoint. The degree of flexibility of this term can be dictated by the particular variable and can be determined based on experience and the associated description herein.

[0111] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each individual member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0112] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include the numerical values explicitly recited as the limits of the range, and also to include all the individual numerical values or sub-ranges encompassed within that range as if the numerical value and sub-range is recited. For example, a weight ratio range of about 1 wt% to about 20 wt% should be interpreted to include the explicitly recited limits of 1 wt% and about 20 wt%, and also to include individual weights such as 2 wt%, 11 wt%, 14 wt%, and sub-ranges such as 10 wt% to 20 wt%, 5 wt% to 15 wt%, etc.

[0113] As used herein by themselves or in conjunction with another term or terms, "alkyl" and "alkyl group” refer to a branched or unbranched saturated hydrocarbon chain. Unless specified otherwise, alkyl groups typically contain 1-10 carbon atoms, such as 1-6 carbon atoms or 1-4 carbon atoms or 1-3 carbon atoms, and can be substituted or unsubstituted. Examples include methyl, ethyl, n-propyl, i- propyl, n-butyl, i-butyl, s-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n- decyl, isopropyl, tert-butyl, and isobutyl.

[0114] As used herein by themselves or in conjunction with another term or terms, “aryl” and “aryl group" refer to phenyl and 7-15 membered bicyclic or tricyclic hydrocarbon ring systems, including bridged, spiro, and/or fused ring systems, in which at least one of the rings is aromatic. Aryl groups can be substituted or unsubstituted. Unless specified otherwise, an aryl group may contain 6 ring atoms (i.e., phenyl) or a ring system containing 9 to 15 atoms, such as 9 to 11 ring atoms, or 9 or 10 ring atoms. Representative examples include naphthyl, indanyl, 1, 2,3,4- tetrahydronaphthalenyl, 6,7,8,9-tetrahydro-5H-benzocycloheptenyl, and 6, 7,8,9- tetrahydro-5H-benzocycloheptenyl. [0115] As a further note, in the present disclosure, it is noted that when discussing the fluids, materials, and methods described herein, these discussions can be considered applicable to the various examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, in discussing details about the methods of making 3D printed objects, such discussion also refers to the 3D printing kits, and vice versa.

Claims

1. A fusing agent for 3D printing, said fusing comprising: a hydroxyphenyl benzotriazole, an surfactant, and water.

2. The composition of claim 1 , which comprises about 1 to about 15 weight % of hydroxyphenyl benzotriazole.

3. The composition of claim 1 , which comprises about 10 to about 50 weight % surfactant.

4. The composition of claim 1 , wherein the surfactant comprises octyl acetate.

5. The composition of claim 1 , wherein the weight ratio of the hydroxyphenyl benzotriazole to surfactant is about 1 :1 to about 1 :10.

6. The composition of claim 1 , which further comprises an organic solvent.

7. The composition of claim 6, wherein the organic solvent is present in an amount of about 20 to about 70 weight % of the total weight of the fusing agent.

8. The composition of claim 6, wherein the organic solvent is selected from at least one of alcohol, glycol and a glycol ether.

9. The composition of claim 1 , which comprises about 10 to 50 weight % water.

10. The composition of claim 1, wherein the hydroxyphenyl benzotriazole is 2-(2- hydroxyphenyl)-2h-benzotriazole.

11. A 3D printing kit comprising powder bed material, and fusing agent, said fusing agent comprising a hydroxyphenyl benzotriazole, surfactant and water.

12. The kit of claim 11 , wherein the powder bed material comprises polyamide.

13. A method for printing a 3D printed object, said method comprising selectively applying fusing agent to powder bed material, and irradiating the selectively applied fusing agent with UV radiation to fuse at least a portion of the powder bed material, wherein the fusing agent comprises a hydroxyphenyl benzotriazole, surfactant and water.

14. The method of claim 13, wherein the UV radiation has a wavelength of about 300 to 400 nm.

15. The method of claim 14, wherein the UV radiation is provided by a UV LED source having a wavelength of 365 nm or 395 nm.